Frequency sensitive device



Oct. .24, 1967 Filed June 8. 1965 T. G. ROHNER FREQUENCY SENSITIVE DEVICE 2 Sheets-Sheet 1 OUTPUT FIG. I

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ATTO RN E Y THOMAS G. BONNER Oct. 24,

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v VOLTAGE INVENTOR. THOMAS G. ROHNER ATTORNEY United States Patent 3,349,256 FREQUENCY SENSITIVE DEVICE Thomas G. Rohner, Minneapolis, Minn assignor to Electric Machinery Mfg. Company, Minneapolis, Mmn., a corporation of Minnesota Filed June 8, 1965, Ser. No. 462,178 6 Claims. (Cl. 307-885) ABSTRACT OF THE DISCLOSURE ceeds the direct-current voltage.

The herein disclosed invention relates to frequency discriminators and has for an object to provide a device which will produce a signal when the frequency of alternating current in a circuit varies from a given predetermined frequency.

Another object of the invention resides in providing a device which will operate when the length of one cycle of the frequency is greater than the length of the cycle of the predetermined frequency.

A still further object of the invention resides in providing a discriminator which will produce a resulting Signal within the period of one cycle.

An object of the invention resides in providing a sawtooth generator producing a voltage having a saw-tooth wave form starting at zero voltage substantially at the beginning of each normal cycle and reaching a predetermined maximum voltage at the end of each normal cycle and a greater voltage with a cycle of the frequency tested of greater length than the length of the cycle of the predetermined normal frequency.

Another object of the invention resides in providing means producing a direct current having a fixed voltage a trifle higher than the maximum saw-tooth voltage when the frequency is normal.

A still further object of the invention resides in providing a sensing circuit for matching the maximum sawtooth voltage with the fixed voltage and deriving a signal therefrom when the maximum saw-tooth voltage exceeds the direct current voltage.

In the control of synchronous motor driven flywheel motor generator set the energy stored in the flywheel serves to maintain the generator speed within prescribed frequency limits for a prescribed length of time even if the line voltage fails completely. It is characteristic of a synchronous motor that upon voltage failure it will act as a generator which attempts to supply power for all the other loads on the line. It hence becomes imperative that the motor be disconnected from the line with practically no delay. It is possible that the load thus placed on the motor operating as a generator ,be several times the normal load for which the motor is designed. The motor should hence be disconnected in the shortest possible time.

the voltage returns, the line voltage and motor voltage will be out of phase causing a severe reverse power transient which will trip open the motor contractor at a time when it may be carrying a current greatly in excess of its rated current. This requires increased current carrying capacity of the relay and increased sturdiness of the whole structure to stand the torque shock involved. The instant invention provides a construction overcoming the disadvantages of the system utilizing a reverse power relay.

In the drawings:

FIG. 1 is a wiring diagram of a frequency discriminator illustrating an embodiment of the instant invention.

FIGS. 2 through 11 are charts showing the voltages of the embodiment of the invention illustrated at the designated localities and plotted against time.

For the purpose of illustrating the invention, an alternating current three phase line L has been shown having conductors, L1, L2 and L3. A three phase synchronous motor 14 is also shown having a running winding not illustratetl but connected to the line L by means of con ductors 15, 16 and 17. The field winding 19 of the motor is connected to any source of direct current as is the usual practice and the motor is also provided with a starting device not shown.

The invention comprises a number of circuits interrelated as follows:

A power supply A is energized from the line L and from the generator action of motor 14 when the line current fails. A phase shift circuit B is energized by alternating current derived from line L and produces a sine wave lagging by a small amount the sine wave of the current energizing said phase shift circuit. The current derived from the modified wave form is fed to a pulse generator C which converts the current into a voltage having a saw-tooth wave form increasing in amplitude during each full cycle of the modified current. A sensing circuit D matches the maximum value of the voltage of the said saw-tooth voltage with a reference voltage produced by power supply A. If the maximum saw-tooth voltage exceeds the reference voltage a pulse is produced by the sensing circuit D which is amplified by an amplifier and which actuates an output circuit F. This output circuit may operate a relay or any mechanism for disconnecting the motor from the line or preventing injury to the same.

has a center tap 25 which is connected by means of a conductor 26 to a ground conductor 27. The ends of the secondary 22 have connected to them conductors 28 and 29 which in turn are connected to diode rectifiers 31 and 32. These rectifiers are further connected together by means of conductors 33 and which are connected to a conductor 34. This latter conductor is connected to a resistor 35. This resistor is connected by a conductor 36 to the collector of a transistor 37. The emitter of this transistor is connected to a common conductor 38 and which furnishes direct current to various parts of the invention. A resistor 41 is connected by means of a conductor .42 to the conductor 36. This resistor is further connected by means of a conductor 43 to a Zener diode 44. Diode 44 is connected by a conductor 45 to the ground conductor 27. A conductor 46 is connected to the conductor 43 and to the base of the transistor 37. A capacitor 48 is connected by means of a conductor 47 to the common conductor 38. This capacitor is further connected by means of a conductor 51 to the ground conductor 27 A similar capacitor 52 is connected by means of a conductor 53 to the conductor 34 and by means of a conductor 54 to the ground conductor 27. By means of this construction, a power supply is provided which furnishes regulated voltage to the conductors 38 and 27 The phase shift circuit B consists of a resistor 55 which is connected at one end by means of a conductor 56 to the conductor 28 leading from the secondary 22 of transformer 28. This resistor is further connected by a conductor 57 to a capacitor 58. Capacitor 58 is connected by a conductor 61 to the ground conductor 27.

The pulse generator C includes a resistor 65 which is connected by means of a conductor 66 to the conductor 57. This resistor is further connected by means of a conductor 67 to the base of a transistor 68. The emitter of this transistor is'connected by means of a conductor 71 to the ground conductor 27. The collector of transistor 68 is connected by a conductor 72 to one end of a resistor 73 and which is connected to the conductor 38 by means of a conductor 74. The resistor 65 is connected by'means of a conductor 75 to a diode 76 which is connected by a conductor 77 to the ground conductor 27 The pulse generator C further includes another transistor 78. The base of this transistor is connected by means of a conductor 79 to a resistor 81 which in turn is connected by a conductor 82 to the conductor 38. A capacitor 83 is connected between the conductor 72 and 79. The emitter of the transistor 78 is connected by a conductor 84 to a resistor 85 and which in turn is connected by means of a conductor 86 to a diode 87. Diode 87 is connected by a conductor 88 to the conductor 29 leading from the secondary 22 of transformer 20. A capacitor 152 is connected across the conductor 84 and the ground conductor 27 by means of conductors 153 and 154. Likewise, two diodes 156 and 157 are connected in series across conductor 84 and ground conductor 27 by mean of conductors 158 and 159. A conductor 91 is connected to the conductor 86 and to another diode 92. This diode in turn is connected by a conductor 93 to the conductor 56. The collector of the transistor 78 is connected by means of a conductor 94 to a resistor 95 and which in turn is connected by a conductor 96 to the conductor 38. Conductor 94 is also connected through a conductor 97 to the base of a at ransistor 98. The emitter of this transistor is connected by a conductor 101 to the ground conductor 27. The collector of the ransistor 98 is connected by means of a conductor 102 to a resistor 103 which in turn is connected by a conductor 104 to the common conductor 38.

The sensing circuit D utilizes a source of constant voltage which serves as a reference voltage and which is produced by a reference circuit 100. This circuit includes a fixed resistor 105 which is connected by means of a conductor 106 to the ground conductor 27. This resistor is further connected by a conductor 107 to a temperature controlled resistor 108 known in the trade as a T hermister. Thermister 108 is connected by a conductor 109 to another fixed resistor 111. This resistor is connected by a conductor 112 to the common conductor 38. The resistors 105, 108 and 111 form a voltage divider and which furnishes a reference voltage fed to the sensing circuit D.

The sensing circuit D utilizes a timer comprising a capacitor 114 and a number of resistors 115, 116, and 117 connected in a series by means of conductors 118 and 119. The resistor 117 is connected to the common conductor 38 by means of a conductor 122. The resistor is connected by means of a conductor 123 to a capacitor 114. This capacitor is in turn connected by means of a conductor 124 to the ground conductor 27.

The sensing circuit D further includes twosilicon controlled switches 113 and 121. The anode gate of the switch 113 is connected by a conductor 125 to the conductor 109. The anode of this switch is connected by means of a conductor 126 to a resistor 127 which in turn is connected by means of a conductor 130 to another conductor 131. This conductor is connected to the conductor 123 of the timer 110 and to a diode 129. The cathode of silicon controlled switch 113 is connected by a conductor 133 to the cathode gate of silicon controlled switch 121. The cathode of this switch is connected by means of a conductor 134 to the ground conductor 27. The anode of the silicon controlled switch 121 is connected by means of a conductor 135 to a conductor 132 which is connected to the conductor 102 and to the diode 129. The anode gate of silicon controlled switch 121 is connected by means of a conductor 136 to a resistor 137 which in turn is connected by means of a conductor 138 which serves as the output conductor of the sensing circuit D. Another resistor 139 is connected by means of a conductor 140 to the conductor 138 and by'means of a conductor 120 to the common conductor 38.

The amplifier circuit E utilizes a transistor 141 whose collector is connected by means of a conductor 142 to a resistor 143. This resistor is connected by a conductor 144 to another resistor 178 which in turn is connected by a conductor 179 to the ground conductor 27. Conductor 138 is connected to the base of transistor 141 While the emitter thereof is connected by means of a conductor 183 to two diodes 184 in series and which are connected to the common conductor 38. A resistance 181 is connected by a conductor to the ground conductor 27 and by a conductor 185 to the conductor 183.

The output circuit F includes a silicon controlled ectifier 145. The cathode of this rectifier is connected by means of a conductor 146 to the ground conductor 27. A conductor 147 connects the anode of this rectifier to a diode 148 which in turn has connected to it a conductor 149 which is connected to conductor L1 of line L. A conductor 151 connects the gate of silicon controlled rectifier 145 to conductor 144. The silicon controlled rectifier 145 controls the operation of a relay 186 which has a coil 187 connected at one end by means of a conductor 188 to the ground conductor 27 and at its other end by means of a conductor 1 89 to the conductor L2 of line L. This relay closes a circuit not shown through contacts 191 and 192 which disconnects the motor 14 from the line L.

To assist in the explanation of the operation of the invention, a number of charts, FIGS. 2 through 11, have been employed in which the voltage at various points in the various circuits are plotted against time. In FIG. 2, the chart shows the voltage curve 161 between conductors L1 and L2 as derived from line L before and after modification due to reduction in frequency caused by the line being disconnected from the source of power. In the following the first cycle is shown as being of proper length while the second cycle is shown as of increased length due to reduction in frequency in the line.

The operation of the invention is as follows:

The power supply A is conventional and consists of the isolating transformer 20 whose primary 21 is connected to the AC. line energizing motor 14. The secondary is center tapped and furnishes pulsating direct current by virtue of the diodes 31, 32, 87 and 92, which current is smoothed out by resistors 35 and 85 and capacitors 48, 52 and 153. The Zener diode 44 and the transistor 37 provide regulated DC. voltage between the common conductor 38 and the ground conductor 27.

The phase shift circuit B is energized by AC. current from conductors 56, 28 and the common ground conductor 27 and conductor 26. Resistor 55 and capacitor 58 operate to produce a phase delay in the voltage, the delayed voltage being indicated at 162 on FIG. 3 and being the voltage between point Z (FIG. 1) and the ground conductor 27. This voltage is delayed during each cycle by an amount indicated by reference numeral 163 in FIG. 3. 1

Voltage 162 is impressed on the base of transistor 68.

which produces an output voltage 164 (FIG. 4) from the collector of said transistor between the point Y and the ground conductor 27. The transistor 68 serving as a switch passes the positive cycles 165 of voltage 164 when the voltage at point Z is negative, and suppresses the negative voltages to a negligible value when the voltage at oint Z is positive. It will be noted that the end of each positive pulse extends into the beginning of each following cycle.

The circuit comprising the capacitor 114 and the resistors 115, 116 and 117 produces a voltage 166 of sawtooth form which is shown in FIG. 7, and represents the voltage between point X and the ground terminal 27. This voltage is impressed on the anode of silicon controlled switch 113 and is indicated by the reference numeral 167 in FIG. 7.

The silicon controlled switch 113 feeds the other silicon controlled switch 121 by conductor 133 which is connected from the cathode of switch 113 to the cathode gate of switch 121.

While transistor 68 is turned ofi (FIG. 4), capacitor 83 will be charged up with a positive pulse which will be added to the voltage across resistor 81 and transistor 78 remains turned on. The resulting voltage between point W and the ground conductor 27 is indicated at 169 in FIG. 5 as a negative voltage. This voltage is negative with respect to ground conductor 27 but positive with respect to the emitter of transistor 78 so that transistor 78 conducts. When transistor 68 turns on capacitor 83 is discharged.

As capacitor 83 dis-charges a negative pip 168, FIG. 5, occurs in the voltage 169 between the base of transistor 78 and ground conductor 27. This pip drives the base of transistor 78 negative with respect to its emitter thus turning it oil for the period of discharge of capacitor 83. The voltage between point V and the ground conductor 27 is still a negative voltage indicated by the reference numeral 171, but the pip 163 has become a square wave pulse 172 as shown in FIG. 6. This pulses rises above the ground level of ground conductor 27. The voltage between point U and ground conductor 27 is indicated by the reference numeral 173 in FIG. 7 and the pulse 172 terminates the voltage 173 for a short interval as indicated at 174. The conductor 102 being connected to the anode of silicon controlled switch 121 opens said switch, if it has been turned on previously, at the beginning of the cycle when the voltage is cut off as indicated at 174. At the same time capacitor 114 is discharged and the saw-tooth wave form 166 is reduced to zero and at the end of the interval 174 commences to increase and continues to increase until chopped olT at the next interval 174.

When the saw-tooth voltage 166 exceeds the regulated direct current voltage 167 (FIG. 7) the silicon controlled switch 113 fires and a negative pulse 175 is formed in the voltage curve 176 between point T and the ground conductor 27 as shown in FIG. 8. This pulse is negative compared to voltage 176.

The pulse 177 is amplified by transistor 141 and inverted so that the same appears as a positive pulse across point S and the ground conductor 27, FIG. 9. The voltage on the gate of the silicon controlled rectifier 145 normally being below that required to fire said rectifier full voltage occurs across the anode-cathode of said rectifier. Due to diode 148 the voltage becomes a positive half wave spaced sine pulses 191 as shown in FIG. 10. When the rectifier 145 fires the pulse 177 becomes a pip 192 shown in FIG. and the voltage 193 following said pip becomes a minimum. At the same time current flows through said rectifier and also through the coil 187 of relay 186. The voltage producing such current is indicated by the pulse 194 in FIG. 11. When relay 186 is energized current flows through contacts 191 and 192 of said relay and disconnects the motor from the line.

The advantages of the invention are manifest. Motors can be produced having windings carrying less current than heretofore possible. Also less flywheel weight will be required. The frequency discriminator forming the subject matter of the instant invention will operate in a matter & of a second or one cycle of alternating current of 60 cycles per second. The instant invention prevents dangerous mechanical shock to the motor and system.

Changes in the specific form of the invention as herein described may be made within the scope of what is claimed without departing from the spirit of the invention.

Having described the invention, what is claimed as new and desired to be protected by Letters Patent is:

I claim:

1. An alternating current frequency discriminator for use with an alternating current line producing a given alternating-current cycle and having a load energized thereby and requiring deenergization upon failure of the alternating current, said discriminator comprising:

(a) means for producing a voltage of saw-tooth form having a sloping leading edge and a substantially vertical trailing edge and with repeating pulses,

(b) means for terminating the voltage pulses at the end of each full alternating-current cycle, the maximum value of the voltage of each pulse varying in correspondence with the length of the cycle,

(0) a power supply for producing a direct current regulated voltage of a higher value than the maximum value of a normal pulse of the saw-tooth voltage,

(d) sensing means for matching the maximum voltage of each pulse with the direct current voltage,

(e) means operated by said sensing means for producing a voltage signal when the saw-tooth voltage exceeds the direct current voltage, and

(f) an output circuit operated by said signal.

2. An alternating current frequency discriminator for use with an alternating current line producing a given alternating-current cycle and having a load energized thereby and requiring deenergization upon failure of the alternating current, said discriminator comprising:

(a) means for producing a voltage of saw-tooth form with repeating pulses,

(b) means for terminating the voltage pulses at the end of each full alternating-current cycle, the maximum value of the voltage of each pulse varying in correspondence with the length of the cycle,

(0) a power supply for producing a direct current regulated voltage of a higher value than the maximum value of a normal pulse of the saw-tooth voltage,

(d) sensing means for matching the maximum voltage of each normal pulse of the saw-tooth voltage with the direct current voltage, said sensing means includ- (e) a silicon controlled switch,

(f) means operated by said switch for producing a voltage signal where the saw-tooth voltage exceeds the direct current voltage, and

(g) an output circuit operated by said signal.

3. An alternating current frequency discriminator for use with an alternating current line producing a given alternating-current cycle and having a load energized thereby and requiring deenergization upon failure of the alternating current, said discriminator comprising:

(a) means for producing a voltage of saw-tooth form with repeating pulses,

(b) means for terminating the voltage pulses at the end of said alternating-current cycles, the maximum value of the voltage of each pulse varying in correspondence with the length of the cycle,

(c) a power supply for producing a direct current regulated voltage of a higher value than the maximum value of a normal pulse of the saw-tooth voltage,

(d) sensing means for matching the maximum voltage of each normal pulse of the saw-tooth voltage with the direct current voltage, said sensing means includ- (e) a silicon controlled switch whose anode is subject to the saw-tooth voltage and whose anode gate is subject to the direct current voltage,

(f) means operated by said switch for producing a voltage signal where the saw-tooth voltage exceeds the direct current voltage, and

(g) an output circuit operated by said signal.

4. An alternating current frequency discriminator for use with an alternating current line producing a given alternating-current cycle and having a load energized thereby and requiring deenergization upon failure of the alternating current, said discriminator comprising:

(a) means for producing a voltage of saw-tooth form with repeating pulses,

(b) means for terminating the voltage pulses at the end of said alternating-current cycles, the maximum value of the voltage of each pulse varying in correspondence with the length of the cycle,

() a power supply for producing a direct current regulated voltage of a higher value than the maximum value of a normal pulse of the saw-tooth voltage,

(d) sensing means for matching the maximum voltage of each normal pulse of the saw-tooth voltage with the direct current voltage, said sensing means includ- (e) a silicon controlled switch Whose anode is subject to the saw-tooth voltage and Whose anode gate is subject to the direct current voltage,

(f) an output circuit, and

(g) a second silicon controlled switch Whose anode gate is connected to the cathode of said first silicon controlled switch and whose cathode gate is connected to said output circuit.

5. An alternating current frequency discriminator for use with an alternating current line producing a given alternating-current cycle and having a load energized thereby and requiring deenergization upon failure of the alternating current, said discriminator comprising:

(a) means for producing a voltage of saw-tooth form with repeating pulses, a single pulse for each complete cycle,

(b) means for terminating the voltage pulses at the end of each full alternating-current, the maximum value of the voltage of each pulse varying in correspondence with the length of the cycle,

(c) a power supply for producing a direct current regulated voltage of a higher value than the maximum value of a normal pulse of the saw-tooth voltage,

(d) sensing means for matching the maximum voltage of each pulse with the direct current voltage,

(e) means operated by said sensing means for producing a voltage signal when the saw-tooth voltage exceeds the direct current voltage, and

(f) an output circuit operated by said signal including (g) a silicon controlled rectifier, and r (h) means for producing from said power supply a voltage in said output circuit across the gate and cathode of said silicon controlled rectifier at the beginning of each cycle suflicient to fire said silicon controlled rectifier and energize said output circuit.

6. An alternating current frequency discriminator for use with an alternating current line producing a given alternating-current cycle and having a load energized thereby and requiring deenergization upon failure of the alternating current, said discriminator comprising:

(a) means for producing a voltage of saw-tooth form with repeating pulses,

(b) means for terminating the voltage pulses at the end of said alternating-current cycles, the maximum value of the voltage of each pulse varying in correspondence with the length of the cycle,

(0) a power supply for producing a direct current regulated voltage of a higher value than the maximum value of a normal pulse of the saw-tooth voltage,

(cl) sensing means for matching the maximum voltage of each pulse with the direct current voltage,

(e) means operated by said sensing means for producing a voltage signal when the saw-tooth voltage exceeds the direct current voltage,

(f) an output circuit operated by said signal including (g) a silicon controlled rectifier,

(h) a pulse generator including (i) a transistor,

(j) a timing circuit having a capacitor and a resistor connected in series and controlling the passage of current through said transistor, and

(k) means energized by said transistor for producing from said power supply a voltage in said output circuit at the beginning of each cycle sufficient to fire said silicon controlled rectifier.

References Cited UNITED STATES PATENTS 2,915,648 12/1959 Chudleig et al. 307--88.5 3,183,372 5/1965 Chin 30788.5 3,209,212 9/1965 Billings 32478 X 3,274,500 9/1966 Bengston 328- X ARTHUR GAUSS, Primary Examiner.

J. A. JORDAN, Assistant Examiner. 

1. AN ALTERNATING CURRENT FREQUENCY DISCRIMINATOR FOR USE WITH AN ALTERNATING CURRENT LINE PRODUCING A GIVEN ALTERNATING-CURRENT CYCLE AND HAVING A LOAD ENERGIZED THEREBY AND REQUIRING DEENERGIZATION UPON FAILURE OF THE ALTERNATING CURRENT, SAID DISCRIMINATOR COMPRISING: (A) MEANS FOR PRODUCING A VOLTAGE OF SAW-TOOTH FORM HAVING A SLOPING LEADING EDGE AND A SUBSTANTIALLY VERTICAL TRAILING EDGE AND WITH REPEATING PULSES, (B) MEANS FOR TERMINATING THE VOLTAGE PULSES AT THE END OF EACH FULL ALTERNATING-CURRENT CYCLE, THE MAXIMUM VALUE OF THE VOLTAGE OF EACH PULSE VARYING IN CORRESPONDENCE WITH THE LENGTH OF THE CYCLE, (C) A POWER SUPPLY FOR PRODUCING A DIRECT CURRENT REGULATED VOLTAGE OF A HIGHER VALUE THAN THE MAXIMUM VALUE OF A NORMAL PULSE OF THE SAW-TOOTH VOLTAGE, (D) SENSING MEANS FOR MATCHING THE MAXIMUM VOLTAGE OF EACH PULSE WITH THE DIRECT CURRENT VOLTAGE, (E) MEANS OPERATED BY SAID SENSING MEANS FOR PRODUCING A VOLTAGE SIGNAL WHEN THE SAW-TOOTH VOLTAGE EXCEEDS THE DIRECT CURRENT VOLTAGE, AND (F) AN OUTPUT CIRCUIT OPERATED BY SAID SIGNAL. 